Chemical attraction of newly hatched oyster drills

Response of newly hatched, predatory snails to competing chemical cues from co-occurring species of prey were determined in laboratory experiments. Egg capsules of Urosalpinx cinerea were collected from an intertidal, vertically zoned community of prey species. The most prevalent prey were barnacles Semibalanus balanoides and Balanus eburneus, oysters Crassostrea virginica, mussels Mytilus edulis, and bryozoans Membranipora tenuis and Schizoporella irrorata. Snail chemotaxis evoked by barnacle odor alone and barnacle odor mixed with odor of either mussels or oysters was assayed in an activity chamber. Mussel odor inhibits chemotaxis to barnacles, but does not evoke chemotaxis itself. Oyster odor inhibits chemotaxis to high concentrations of barnacle odor, but increases chemotaxis to low concentrations of barnacle odor. Chemotaxis to barnacle odor is reduced by 2 h pre-exposure to either barnacle, oyster, or mussel odors. Such cross-adaptation suggests that inhibition or facilitation of chemotaxis in odor mixtures is not caused by one odor masking a second while free in the sea water. We infer that newly hatched snails integrate chemical information in barnacle-oyster and barnacle-mussel odor mixtures. These results, and those of earlier investigations, suggest a behavioral explanation for vertical distribution of juvenile U. cinerea in the intertidal zone.